Currently I am a vegetarian because I still take whey protein. But I will become vegan once my pea/rice protein gets here. I heard that people who switch to vegan lose some size initially. Is this true?

I gained 6 additional pounds on my bulk switching to veganism. If you're already 99% vegan, I doubt switching out your protein powder will make a very noticeable difference in your physique (other than how much food you're eating).

I lost 3 pounds at the beginning because I kept looking in the fridge and not knowing what to eat. I figured it out pretty quick tho and now have a whole bunch of new favorite foods and recipes . Now I have to be careful not to eat too much.

If it's important to you, you'll find a way. If it isn't, you'll find an excuse.

that's good to know. I just heard that former meat eaters tend to lose some weight when they go through the detox phase of the vegan diet. I have been a meat eater for most of my life. Just recently switch to vegetarianism and soon to be vegan.

I actually gained roughly 60 lbs. after going vegan, but that was over a 3-4 year stretch

Didn't have any "detox" effect despite going from someone who ate meat at EVERY meal and pretty well zero vegetables before going vegan. Just kept the same weight for a little bit, then when I started training for powerlifting I gained a lot of weight, and another 30 lbs. when I got into strongman for a bit. If you eat enough, you won't lose any mass!

"A 'hardgainer' is merely someone who hasn't bothered to try enough different training methods to learn what is actually right for their own damned body." - anonymous